This invention is in the field of electrochemical processes and apparatus. More specifically, the present invention is directed to the divided electrochemical cell synthesis and production of Group IV and V volatile hydrides with the simultaneous counter production of oxygen, and a reactor for carrying out the synthesis. The synthesis and the reactor are designed to more efficiently produce high purity hydrides substantially free of oxygen.
High purity gases are required for semiconductor fabrication and doping. Often these gases are dangerously toxic. Commercial compressed gas cylinders store gas at several thousand pounds per square inch pressure and contain one to ten pounds of gas. Hence, centralized production, transportation, and storage of these materials present a hazard to those working with them.
To avoid these hazards, an apparatus has been developed to provide these dangerous gases to be generated only when they are needed; such as at a chemical vapor deposition reactor in a semiconductor manufacturing plant. For example, W. M. Ayers, in U.S. Pat. Nos. 5,158,656 and 6,080,297, describes an electrochemical apparatus and method for supplying volatile hydrides at the proper pressure for introduction into a chemical vapor deposition reactor. Such processes generate metal hydride gas and hydrogen gas from the corresponding metal cathode by employing a sacrificial anode (i.e., an electrode that corrodes to an oxide) and hydroxide-based electrolytes in an undivided electrochemical cell. Such processes, however, are economically unattractive for high volume production due to high cost of the sacrificial anode metal such as molybdenum and tungsten.
Porter, in U.S. Pat. No. 4,178,224, discloses an electrochemical method for the synthesis of arsine gas that utilizes a dissolved arsenic salt in an acidic electrolyte with an oxygen evolving anode. With this method, however, the arsine concentration was limited to less than 25%. Another limitation of Porters method was the need to balance pressures and liquid levels in the divided anode and cathode sections of the electrochemical cell. This requires an inert gas supply to the electrochemical process.
Bouard, in U.S. Pat. No. 5,425,857, discloses an electrochemical process utilizing an electrolyte containing arsenic salts and acid which operates in a divided electrochemical, generating arsine and hydrogen in the cathode chamber, and oxygen in the anode chamber. The process in burdened by the need to use auxiliary gas separation tanks and multiple pumps. In addition the simultaneous metering and addition of both acid and arsenic salt is required to maintain the process.
U.S. Pat. Nos. 5,427,659, and 5,474,659, disclose the electrochemical generation of hydride gases with aqueous electrolytes under conditions that avoid oxygen formation. The hydride yield is much lower than desired.
Thus, while efforts have continued to provide effective means for producing and delivering hydride gases, there is still a need in the art to improve the quality and quantity of delivered hydride gas, especially, hydrides substantially free of oxygen product streams.